Reactive dyes have become a concern of the EPA. Currently, methods are being sought to characterize and identify these reactive dyes and their transformation products, in order to predict their transport, transformation and potential fate and effects in receiving waters. Reactive Blue 19 (RB 19), its reactive form (RB 19-VS) and its hydrolyzed form (RB 19-OH) were examined using liquid secondary ion mass spectrometry/tandem mass spectrometry (LSIMS/MS/MS) in the negative-ion mode under low-energy collision conditions (240-300 eV). Structurally characteristic fragment ions were obtained, none of which has been previously reported for these reactive dyes. Among the ions obtained were SO3(-) ions, ions due to central amino cleavage and reactive group cleavage, and ions due to loss of SO3 and SO2. Possible pathways for the formation of product are proposed. The structural information obtained should help to characterize and identify reactive dyes better.